Rotating electrical machine plants

ABSTRACT

The present invention relates to installations for transformerless generation of HVDC and wherein the installation comprises rotating high-voltage single-winding/multiple-winding machines and converters. The single-winding/multiple-winding machine comprises a magnetic circuit with one or more magnetic cores and one or more windings, phase-shifted in space, which comprise a cable with one or more current-carrying conductors ( 2 ), each conductor comprising a number of strands, around each strand there being arranged an inner semiconducting layer ( 3 ), around which is arranged an insulating layer ( 4 ) of solid insulation, around which is arranged an outer semiconducting layer ( 5 ).

TECHNICAL FIELD

[0001] The present invention relates to installations fortransformerless generation of HVDC (high-voltage direct current) andwherein the installation comprises a rotating high-voltagesingle-winding or multiple-winding machine and a converter. Theinvention also comprises devices for high-voltage electric machineoperation with a variable speed. In practice, this means that theinstallations convert a mechanical torque into direct current and directvoltage without intermediate transformers, and that the installationsconvert direct current and direct voltage into mechanical torque withoutintermediate transformers.

[0002] The single-winding or multiple-winding machine comprises amagnetic circuit with one or more cores of laminated, normal ororiented, sheet or other, for example amorphous or powder-based,material, or any other action for the purpose of allowing an alternatingflux, one or more winding systems, cooling systems, etc., which may bedisposed in the stator or the rotor of the machine, or in both.

[0003] The single-winding or multiple-winding machine may also be madeas an air-gas-wound machine Without magnetic material or with magneticmaterial only in the back portion.

[0004] The invention also comprises methods for manufacturing magneticcircuits for a rotating high-voltage single-winding/multiple-windingmachine.

BACKGROUND ART, THE PROBLEM

[0005] As mentioned under the “Technical Field”, devices according tothe invention are primarily intended to be part of installations fortransformerless generation of high-voltage direct current and forhigh-voltage electric machine drives. Installations where the inventionwill be used normally lie within the power range of 1 MW to 15 GW andcomprise one or several rotating machines.

[0006] Within electronic power engineering there is a technical fieldwhich is currently referred to as power electronics. This expressioncorresponds to the German “Leistungselektronik” and is sometimes stillcalled “Stromrichtertechnik” in German. The field comprises conversionof electric power between different forms, such as conversion between

[0007] DC and AC, inverter operation

[0008] AC and DC, rectifier operation

[0009] AC and AC corresponds to ac conversion/ac conversion with anarbitrary ratio between the frequency, amplitude, phase position andphase number of the voltages, DC and DC corresponds to dc conversion/dcconversion.

[0010] The terminology in this field is unfortunately not quiteconsistent. However, an IEC summary is to be found in “InternationalElectrotechnical Dictionary” and in Publ. IEC 60050-551 IEV “Powerelectronics”.

[0011] There are a very large number of different semiconductorcomponents which may be included in the fields of use which arecomprised by the patent application. One example of the state of the artin this respect is found in “Modern Power Electronics” by Bose et al,IEEE Industrial Electronics Society, ISBN:0-87942-282-3. Among thecomponents mentioned there are:

[0012] thyristors, diodes, triacs, gate turn-off thyristors (GTO),bipolar transistors (BJT) , PWM transistors, MOSFET, insulated gatebipolar transistors (IGBT), static induction transistors (SIT), staticinduction thyristors (SITH), MOS-controlled thyristors (MCT), etc.

[0013] Semiconductor connections for inverter operation andrectification are commonly referred to in English as “converters”. Nounambiguous Swedish correspondence exists. Since that part of theinvention which deals with HVDC power conversion comprises both inverteroperation and rectifier operation, the semiconductor connections underdiscussion will be referred to below as converters.

[0014] For that part of the invention which deals with high-voltageelectric machine drive with a variable speed, the above-mentioned AC/ACpower conversion will be used. Such electric machine drive will bedescribed below both with regard to the state of the art and with regardto the application according to the invention.

[0015] To be able to describe both the technical and economic advantagesand the gains derived by using devices according to the invention, adescription will be given both of how installations for generation ofHVDC and for high-voltage electric machine drive with a variable speedare designed according to the state of the art.

[0016] A conventional HVDC transmitter station is clear from FIG. 1. Inprinciple, it comprises a number of ac generators G1 - - - Gn which,according to the state of the art, have a voltage of 25-30 kV. Viatransformers A1 - - - An, preferably D/Y-connected, the generatorvoltage is stepped up to a suitable ac transmission level and istransmitted over shorter of longer distances via ac transmission linesin a high-voltage ac network. The predominant method for rectificationis then to use so-called 12-pulse rectification. The sine shape in theac network is secured with ac filters near the converters. The 12-pulserectification assumes that consecutively series-connected converterbridges B1 - - - Bn are fed from ac systems which are displaced 30electrical degrees relative to each other. This is achieved byconnecting to the high-voltage ac network Y/Y-connected convertertransformers Y1 - - - Yn and corresponding Y/D-connected convertertransformers D1 - - - Dn, which are allowed to feed the converters.

[0017] Such a conventional HVDC transmitter station thus comprises twotransformer stages, ac filters, ac circuit breakers and an ac busbarsystem. Because the transformers are normally intended for transmissionof high powers, they are normally oil-cooled and oil-insulated. Becauseof the series-connected converters, the windings and the bushings of theconverter transformers will be subjected to a rising dc potential,counting from ground. It places very heavy demands on the insulation andthe bushings of these transformers. This is describes, inter alia, in“Power Transmission by Direct Current” by E. Uhlmann, Springer Verlag1975, pp. 327-328, in ELECTRA No. 141, April 1992, pp. 34-39, and inELECTRA No. 155, August 1994, pp. 6-30.

[0018] An HVDC transmission according to the one described above isdescribed, inter alia, in an article entitled “The Skageracktransmission”—The world's longest HVDC submarine cable link” in AseaJournal 1980, Vol. 53, Nos. 1-2, pp. 3-12, and in an article “Directconnection of generators to HVDC converters” in ELECTRA No. 149, August1993.

[0019] Recently, an embodiment of an HVDC transmitter station has beendiscussed which comprises direct connection from each generator to theY/Y-connected and the Y/D-connected converter transformers. Such aninstallation is described, inter alia, in the above-mentioned article inELECTRA and is here referred to as a “direct connection”.

[0020] Such a connection is clear from FIG. 2. The voltage from thegenerators G1 - - - Gn is here fed directly to the convertertransformers Y - - - Yn and D1 - - - Dn, respectively. Such a connectionmakes greater demands on the converter transformers since they must nowalso be responsible for the step-up transformation of the voltage of thegenerators to the level corresponding to the desired direct-voltagelevel.

[0021] One problem with such a connection is that converter harmonicsmay give increased losses in the stator windings of the generators.

[0022] To distinguish the present invention from the prior art, it willbe especially pointed out that the “HVDC converter” referred to in theabove-mentioned article in ELECTRA Nol 149 for direct connection to thegenerators comprise the two Y/Y-connected and Y/D-connected convertertransformers, respectively, and the converters.

[0023] There is a special interphase transformer converter connection,which is shown in FIG. 3. In conformity with FIGS. 1 and 2, the supplyof the converters S1 and S2 takes place by means of two three-phasevoltages, displaced by 30 electrical degrees relative to each other, viathe transformers T1 and L2. If the connection otherwise comprises thereactors R1 and R2, no dc potential stress arises on the feedingtransformers or generators. R1 and R2 are often designed with a commoncore and winding as well as a centre tap.

[0024] In the introductory part of the specification it was mentionedthat a device according to the invention comprises asingle-winding/multiple-winding machine. One example of amultiple-winding machine according to the state of the art is describedin U.S. Pat. No. 4,132,914 entitled “Six-phase winding of electricmachine stator”. The windings are here especially formed to obtain aslow voltages as possible between the external connections. The six-phasewindings in this and similar machines are formed as two three-phasewindings which are normally electrically displaced relative to eachother by 30 electrical degrees. This permits a possibility ofsubsequently achieving one single three-phase voltage with the aid of aY-connected and a D-connected transformer.

[0025] The above-mentioned machine and similar machines according to thestate of the art are designed for voltages of up to about 25 kV.Machines with two three-phase windings, electrically displaced relativeto each other by 30 electrical degrees, may be used according to theabove, without intermediate transformers, for 12-pulse rectificationwith converters. With the highest voltage in existing machines, however,the rectified voltage may amount to a maximum of about 30 kV,symmetrically distributed as about +/−15 kV around ground potential.

[0026] Series connection of converters fed from several generators forachieving what is commonly termed HVDC, that is, direct voltages of 100kV and higher, is not possible with generators according to the currenttechnique with mica-based insulation technique because these do notwithstand the dc component to which the generator windings in the mostcommonly used converter connections will be subjected.

[0027] A rotating high-voltage single-winding/multiple-winding machineincluded in an installation according to the invention is able tooperate as a variable-speed motor fed via semiconductor connections froma high-voltage dc network and as a generator to generate an ac networkvia semiconductor connections and transformers.

[0028] Electric machine drives with variable speed for ac machinesaccording to the state of the art assumes, for various practicalreasons, that the machine is provided with two three-phase windingsdisplaced relative to each other by 30 electrical degrees. For the speedcontrol, the machines then have to be supplied with a variablefrequency. The voltage level of the supply according to the state of theart is of the order of magnitude of 5 kV.

[0029] Motor drives of the above-mentioned kind are published in anumber of pamphlets and articles, such as in “High-speed synchronousmotors. Adjustable speed drives”, Asea pamphlet OG 135-101E, “Freqsyn—anew drive system for high-power applications”, Asea Journal 59 (1986):4,pp. 16-19. An order for 100-MW adjustable-speed motors for driving awind tunnel fan has been placed by NASA according to ABB Review 9/1995,p. 38.

[0030] The supply of such motor drives may take place in different ways,for example as a pure AC/AC power conversion or from a direct-voltagenetwork via controllable converters. The construction of such aninstallation is described, inter alia, in an article entitled“Synchronous machines with single or double 3-phase star-connectedwinding fed by 12-pulse load commutated inverter”, published in ICEM 94,International Conference on Electrical Machines, Part Vol. 1, pp.267-272.

[0031] Electric machine drives with a variable speed may also beachieved with machines with a winding system if the supply takes placewhile utilizing the latest technical development, so-called PMWtechnique, that is, with pulse-width modulation and self-commutatedconverters, in which case also a six-pulse connection may be used.

[0032] Regarding somewhat smaller rotating electric machines, theso-called reluctance machines may be mentioned, which are currentlydesigned for up to a few hundred kilowatts, wherein both the stator andthe rotor are provided with salient poles. Such motors are described,inter alia, in “Variable speed switched reluctance motors” in IEE Proc.B, Vol. 127, November 1980, pp. 253-265. The machines are currentlylow-voltage machines and the windings surround the salient poles of thestator in many layers. These reluctance machines are examples ofmachines which may be further developed for connection via converters tohigh dc voltage.

[0033] As will have been clear from the above, the present inventioncomprises a rotating high-voltage single-winding/multiple-windingmachine intended for voltage levels significantly exceeding those whichapply to machines according to the state of the art. This also entailsgreat possibilities for electric machine drives with variable speed atconsiderably higher voltage levels and the advantages this brings withregard to machine power etc.

[0034] To be able to describe the advantages and the inventive stepwhich the invention represents, a description will first be made of thecomposition of such machines according to the state of the art. Thesingle-winding/multiple-winding machine according to the inventionrelates to a machine which is capable of generating a voltage system orseveral voltage systems, phase-shifted in space, with a correspondingwinding system. In all essentials, the composition of the rotatinghigh-voltage single-winding/multiple-winding machine according to theinvention is independent of whether the machine is made as asingle-winding machine or whether it is made as a multiple-windingmachine and whether it is used for HVDC generation or for high-voltagevariable-speed motor drives.

[0035] The state of the art will therefore be described starting from aconventional single-winding machine with a voltage level of about 25-30kV exemplified on the basis of a synchronous machine. The descriptionsubstantially relates to the magnetic circuit of such a machine and howthis is composed according to classic technique. Since the magneticcircuit referred to in most cases is disposed in the stator, themagnetic circuit below will normally be described as a stator with alaminated core, the winding of which will be referred to as a statorwinding, and the slots in the laminated core for the winding will bereferred to as stator slots or simply slots.

[0036] Most synchronous machines have a field winding in the rotor,where the main flux is generated by direct current, and an ac winding inthe stator. The synchronous machines are normally of three-phase design.Sometimes, the synchronous machines are designed with salient poles. Thelatter have an ac winding in the rotor. Sometimes, the machines aredesigned with polyphase windings both in the stator and in the rotor asso-called synchronous flux machines to allow operation at other thansynchronous speeds.

[0037] The stator body for large synchronous machines is often made ofsheet steel with a welded construction. The laminated core is normallymade from varnished 0.35 or 0.5 mm electric sheet. For larger machines,the sheet is punched into segments which are attached to the stator bodyby means of wedges/dovetails. The laminated core is retained by pressurefingers and pressure plates.

[0038] For cooling of the windings of the synchronous machine, threedifferent cooling systems are available.

[0039] In case of air cooling, both the stator winding and the rotorwinding are cooled by cooling air flowing through. The cooling airchannels are to be found both in the stator laminations and in therotor. For ventilation and cooling by means of air, the laminated coreat least for medium-sized and large machines is divided into stacks withboth radial and axial ventilation ducts disposed in the core. Thecooling air may consist of ambient air but at powers exceeding 1 MW, aclosed cooling system with heat exchangers is substantially used. Air isthe substantial medium for hydrogenerators.

[0040] Hydrogen cooling is normally used in turbogenerators up to about400 MW and in large synchronous condensers. The cooling method functionsin the same way as in air cooling with heat exchangers, but instead ofair as coolant there is used hydrogen gas. The hydrogen gas has bettercooling capacity than air, but difficulties arise at seals and inmonitoring leakage.

[0041] For turbogenerators in the power range of 500-1000 MW, it isknown to apply water cooling of both the stator winding and the rotorwinding. The cooling channels are in the form of tubes which are placedinside conductors in the stator winding.

[0042] One problem with large machines is that the cooling tends tobecome non-uniform and that, therefore, temperature differences ariseacross the machine.

[0043] The stator winding is disposed in slots in the laminated core.The slots normally have a cross section as that of a rectangle or atrapezoid. Each winding phase comprises a number of series-connectedcoil groups and each coil group comprises a number of series-connectedcoils. The different parts of the coil are designated coil side for thatpart which is placed in the stator and coil end for that part which isdisposed outside the stator. A coil comprises one or more conductorsbrought together in height and/or width. Between each conductor there isa thin insulation, for example epoxy/glass fibre. The coil is insulatedagainst the slot with a coil insulation, that is, an insulation intendedto withstand the rated voltage of the machine to ground. As insulatingmaterial, various plastic, varnish and glass fibre materials may beused. Usually, so-called mica tape is used, which is a mixture of micaand hard plastic, especially produced to provide resistance to partialdischarges, which can rapidly break down the insulation. The insulationis applied to the coil by winding the mica tape around the coil inseveral layers. The insulation is impregnated, and then the coil side ispainted with a coal-based paint to improve the contact with thesurrounding stator which is connected to ground potential.

[0044] The conductor area of the windings is determined by the relevantcurrent intensity and by the cooling method used. The conductor and thecoil are usually formed with a rectangular shape to maximize the amountof conductor material in the slot. A typical coil is formed of so-calledRoebel bars, in which certain of the bars may be made hollow for acoolant. A Roebel bar comprises a plurality of rectangular,parallel-connected copper conductors, which are transposed 360 degreesalong the slot. Ringland bars with transpositions of 540 degrees andother transpositions also occur. The transposition is made to avoid theoccurrence of circulating currents which are generated in a crosssection of the conductor material, as viewed from the magnetic field.

[0045] In this context, it should also be pointed out that, inconnection with converter operation, harmonics arise in the currents.These harmonics are not distributed uniformly over the rectangular crosssection, which leads to skin effect and increased losses.

[0046] For mechanical and electrical reasons, a machine cannot be madein just any size. The machine power is determined substantially by threefactors:

[0047] The conductor area of the windings. At normal operatingtemperature, copper, for example, has a maximum value of 3-3.5 A/mm².

[0048] The maximum flux density (magnetic flux) in the stator and rotormaterial.

[0049] The maximum electric field strength in the insulating material,the so-called dielectric strength.

[0050] Polyphase ac windings are designed either as single-layer ortwo-layer windings. In the case of single-layer windings, there is onlyone coil side per slot, and in the case of two-layer windings there aretwo coil sides per slot. Two-layer windings are usually designed asdiamond windings, whereas the single-layer windings which are relevantin this connection may be designed as a diamond winding or as aconcentric winding. In the case of a diamond winding, only one coil span(or possibly two coil spans) occurs, whereas flat windings are designedas concentric windings, that is, with a greatly varying coil width. Bycoil width is meant the distance in circular measure between two coilsides belonging to the same coil, either in relation to the relevantpole pitch or in the number of intermediate slot pitches. Usually,different variants of chording are used, for example fractional pitch,to give the winding the desired properties. The type of windingsubstantially describes how the coils in the slots, that is, the coilsides, are connected together outside the stator, that is, at the coilends.

[0051] Outside the stacked sheets of the stator, the coil is notprovided with a painted semiconducting ground-potential layer ofcarbon-based paint. The coil end is normally provided with an E-fieldcontrol in the form of so-called corona protection varnish intended toconvert a radial field into an axial field, which means that theinsulation on the coil ends occurs at a high potential relative toground. This sometimes gives rise to corona in the coil-end region,which may be destructive. The so-called field-controlling points at thecoil ends entail problems in the design of a rotating electric machine.

[0052] Normally, all large machines are designed with a two-layerwinding and equally large coils. Each coil is placed with one side inone of the layers and the other side in the other layer. This means thatall the coils cross each other in the coil end. If more than two layersare used these crossings render the winding work difficult anddeteriorate the coil end.

[0053] During the last few decades, there have been increasingrequirements for rotating electric machines for higher voltages thanwhat has previously been possible to design and manufacture. The maximumvoltage level which, according to the state of the art, has beenpossible to achieve for synchronous machines with a good yield in thecoil production is around 25-30 kV.

[0054] Certain attempts to a new approach as regards the design ofsynchronous machines are described, inter alia, in an article entitled“Water-and-oil-cooled Turbogenerator TVM-300” in J. Elektrotechnika, No.1, 1970, pp. 6-8, in U.S. Pat. No. 4,429,244, “Stator of Generator”, andin Russian patent document CCCP Patent 955369.

[0055] The water- and oil-cooled synchronous machine described in J.Elektrotechnika is intended for voltages up to 20 kV. The articledescribes a new insulation system consisting of oil/paper insulation,which makes it possible to immerse the stator completely in oil. The oilcan then be used as a coolant while a the same time using it asinsulation. To prevent oil in the stator from leaking out towards therotor, a dielectric oil-separating ring is provided at the internalsurface of the core. The stator winding is made from conductors with anoval hollow shape provided with oil and paper insulation. The coil sideswith their insulation are secured to the slots made with rectangularcross section by means of wedges. As coolant oil is used both in thehollow conductors and in holes in the stator walls. Such coolingsystems, however, entail a large number of connections of both oil andelectricity at the coil ends. The thick insulation also entails anincreased radius of curvature of the conductors, which in turn resultsin an increased size of the winding overhang.

[0056] To above-mentioned U.S. Pat. No. 4,429,244 relates to the statorpart of a synchronous machine which comprises a magnetic core oflaminated sheet with trapezoidal slots for the stator winding. The slotsare tapered since the need of insulation of the stator winding issmaller towards the interior of the rotor where that part of the windingwhich is located nearest the neutral point is disposed. In addition, thestator part comprises a dielectric oil-separating cylinder nearest theinner surface of the core. This part may increase the magnetizationrequirement relative to a machine without this ring. The stator windingis made of oil-immersed cables with the same diameter for each coillayer. The layers are separated from each other by means of spacers inthe slots and secured by wedges. What is special for the winding is thatit comprises two so-called half-windings connected in series. One of thetwo half-windings is disposed, centered, inside an insulating sleeve.The conductors of the stator winding are cooled by surrounding oil.Disadvantages with such a large quantity of oil in the system are therisk of leakage and the considerable amount of cleaning work which mayresult from a fault condition. Those parts of the insulating sleevewhich are located outside the slots have a cylindrical part and aconical termination reinforced with current-carrying layers, the duty ofwhich is to control the electric field strength in the region where thecable enters the end winding.

[0057] From CCCP 955369 it is clear, in another attempt to raise therated voltage of the synchronous machine, that the oil-cooled statorwinding comprises a conventional high-voltage cable with the senedimension for all the layers. The cable is placed in stator slots formedas circular, radially disposed openings corresponding to thecross-section area of the cable and the necessary space for fixing andfor coolant. The different radially disposed layers of the winding aresurrounded by and fixed in insulating tubes. Insulating spacers fix thetubes in the stator slot. Because of the oil cooling, an internaldielectric ring is also needed here for sealing the oil coolant againstthe internal air gap. The disadvantages of oil in the system describedabove also apply to this design. The design also exhibits a very narrowsradial waist between the different stator slots, which means a largeslot leakage flux which significantly influences the magnetizationrequirement of the machine.

[0058] A report from Electric Power Research Institute, EPRI, EL-3391,from 1984 describes a review of machine concepts for achieving a highervoltage of a rotating electric machine for the purpose of being able toconnect a machine to a power network without an intermediatetransformer. Such a solution is judged by the investigation to providegood efficiency benefits and great economic advantages. The main reasonthat it was considered possible in 1984 to start developing generatorsfor direct connection to power networks was that at that time asuperconducting rotor had been produced. The large magnetizationcapacity of the superconducting field makes it possible to use an airgap winding with a sufficient thickness to withstand the electricalstresses.

[0059] By combining the most promising concept, according to theproject, of designing a magnetic circuit with a winding, a so-calledmonolith cylinder armature, a concept where two cylinders of conductorsare enclosed in three cylinders of insulation and the whole structure isfixed to an iron core without teeth, it was judged that a rotatingelectric machine for high voltage could be directly connected to a powernetwork. The solution meant that the main insulation had to be madesufficiently thick to cope with phase-to-phase and phase-to-groundpotentials. Obvious disadvantages with the proposed solution are that,in addition to requiring a superconducting rotor, it requires a verythick insulation which increases the size of the machine. The coil endsmust be insulated and cooled with oil or freons to control the largeelectric fields in the ends. The whole machine must be hermeticallyenclosed to prevent the liquid dielectric from absorbing moisture fromthe atmosphere.

[0060] When manufacturing rotating electric machines according to thestate of the art, the winding is manufactured with conductors andinsulation systems in several steps, whereby the winding must bepreformed prior to mounting on the magnetic circuit. Impregnation forpreparing the insulation system is preformed after mounting of thewinding on the magnetic circuit.

SUMMARY OF THE INVENTION, ADVANTAGES

[0061] One object of the invention is to provide installations fortransformerless generation of HVDC and that the installation includes arotating single-winding/multiple-winding machine with such a highvoltage that the transformer stages shown in FIGS. 1 and 2, with step-uptransformation of the generator voltage first to ac transmission highvoltage and tne Y/Y-connected and Y/D-connected transformers,respectively, for achieving 12-pulse rectification with converters, canbe eliminated. Thus, the machine is intended, inter alia, to directlysupply the converters with the high voltage which is needed forachieving an HVDC network. In this context, the difference with respectto the above-mentioned “Direct connection” described in ELECTRA shouldbe noted. It is clear from the above, it is another object of theinvention to provide installations for high-voltage variable-speedelectric machine drives.

[0062] In practice, the above two objects mean that the installationsconvert a mechanical torque, via converters, to direct current anddirect voltage without intermediate transformers, and that theinstallations convert direct current and direct voltage, via converters,to a mechanical torque without intermediate transformers.

[0063] The converters may also comprise one or more of the semiconductordevices which are mentioned under the “Background Art”.

[0064] The introduction of such a single-winding/multiple-windingmachine thus entails considerably lower investment costs and reducedrequirements on space in relation co corresponding HVDC installationsaccording to the state of the art. An HVDC installation according to theinvention also permits the total efficiency of the installation to beincreased. Also with regard to high-voltage variable-speed electricmachine drives, the machine/converter concept according to the followingdescription entails considerable advantages relative to the state of theart.

[0065] A rotating high-voltage single-winding/multiple-winding machineas an integral part of the present invention entails a considerablyreduced thermal stress on the stator. Temporary overloads of the machinethus become less critical and it sell be possible to drive the machineat overload for a longer period of time without running the risk ofdamage arising. This means considerable advantages for owners of powergenerating plants who are forced today, in case of operationaldisturbances, to rapidly switch to other equipment in order to ensurethe delivery requirements laid down by regulations.

[0066] With a rotating high-voltage single-winding/multiple-windingmachine as an integral part of the present invention, the maintenancecosts can be significantly reduced because transformers, on-load tapchangers, circuit breakers, filters, transmission lines, reactors, etc.,do not have to be included in the system.

[0067] To increase the power of a rotating electric machine, it is knownto attempt to increase the current in the ac coils. This has beenachieved by optimizing the quantity of conducting material, that is, byclose-packing of rectangular conductors in the rectangular rotor slots.The aim has been to handle the increase in temperature resulting fromthis by increasing the quantity of insulating material and using moretemperature-resistant and hence more expensive insulating materials. Thehigh temperature and field load on the insulation has also causedproblems with the life of the insulation. In the relatively thick-walledinsulating layers which are used for high-voltage equipment, for exampleimpregnated layers of mica tape, partial discharges, PD, constitute aserious problem. When manufacturing these insulating layers, cavities,pores, and the like, will easily arise, in which internal coronadischarges arise when the insulation is subjected to high electric fieldstrengths. These corona discharges gradually degrade the material andmay lead to electric breakdown through the insulation.

[0068] The great and essential difference between a rotating electricmachine according to the state of the art and the embodiment accordingto the invention is that the magnetic circuit of the rotatinghigh-voltage single-winding/multiple-winding machine comprises one ormore windings, phase-shifted in space, of a threaded or wound cable withone or more solid insulated conductors with a semiconducting layer bothat the conductor and the casing and, between the two semiconductinglayers, a layer with a solid insulation. The outer semiconducting layermay be connected to ground potential.

[0069] If a converter connection according to FIGS. 1 and 2 is used, thesolid insulating layer will be subjected to both ac and dc potentials.If, on the other hand, a converter connection according to FIG. 3 isused, the solid layer will be subjected to ac potential only. The cablewith which the windings in a machine according to the invention is woundmust thus be chosen with regard to the potential stress in question.

[0070] The present invention is based on the realization that, to beable to increase the power of a rotating electric machine in atechnically and economically justifiable way, this must be achieved byensuring that the insulation is not broken down by the phenomenadescribed above. This can be achieved according to the invention byusing as insulation layers made in such a way that the risk of cavitiesand pores is minimal, for example a solid extruded insulating layer of asuitable solid insulating material, such as thermoplastic resins or,alternatively, crosslinked materials such as XLPE or rubber, for exampleEP rubber or silicone rubber, also alternatively crosslinked. Inaddition, it is important that the insulation comprises an inner layer,surrounding the conductor, with semiconducting properties and that theinsulation is also provided with at least one additional outer part,surrounding the solid insulating layer, with semiconducting properties.By using only a solid insulating layer which may be manufactured with aminimum of defects and, in addition, providing the solid layer with aninner and an outer semiconducting part, it can be ensured that thethermal and electric loads are reduced. At temperature gradients, theinsulating part with the semiconducting layers will constitute amonolithic part and defects caused by different temperature expansion inthe solid layer and the surrounding semiconducting layers do not arise.The electric load on the material decreases as a consequence of the factthat the semiconducting parts around the solid insulating layer willconstitute equipotential surfaces and that the electric field in thesolid insulating layer will thus be distributed uniformly over thethickness of the layer. The outer semiconducting layer may be connectedto a ground potential. This means that, for such a cable, the outercasing of the winding in its entire length may be kept at groundpotential.

[0071] The outer layer may also be cut off at suitable locations alongthe length of the conductor and each cut-off partial length may bedirectly connected to a chosen potential, ground potential. Around theouter semiconducting layer there may also be arranged other layers,casings and the like, such as a metal shield and a protective jacket.

[0072] Further knowledge gained in connection with the present inventionis that increased current load leads to problems with voltage (E) fieldconcentrations at the corners at a cross section of a coil and that thisentails large local loads on the insulation there. Likewise, themagnetic (B) field in the tooth of the rotor will be concentrated at thecorners. This means that magnetic saturation arises locally and that themagnetic core is not utilized in full and that the waveform of thegenerated voltage/current will be distorted. In addition, eddy lossescaused by induced eddy currents in the conductors, which arise becauseof the geometry of the conductors in relation to the B field, willentail additional disadvantages at increasing current densities.

[0073] A further improvement of the invention is achieved by making thecoils and the slots in which the coils are placed circular instead ofrectangular. By making the coils circular, these will be surrounded by aconstant B field without concentrations where magnetic saturation mayarise. Also the E field in the coil will be distributed uniformly overthe cross section and local loads on the insulation are considerablyreduced. In addition, it is easier to place circular coils in slots insuch a way that the number of coil sides per coil group may increase andan increase of the voltage may take place without the current in theconductors having to be increased. The reason is that the cooling of theconductors is facilitated by, on the one hand, a lower current densityand hence lower temperature gradients across the insulation and, on theother hand, by the circular shape of the slots which entails a moreuniform temperature distribution over a cross section. Additionalimprovements may also be achieved by composing the conductor fromsmaller parts, so-called strands. The strands may be insulated from eachother and only a small number of strands may be left uninsulated and incontact with the inner semiconducting layer, to ensure that is at thesame potential as the conductor.

[0074] One further development of a conductor composed of strands ispossible in that it is possible to insulate the strands with respect toeach other in order thus to reduce the amount of eddy current losses inthe conductor. One or a few of the strands may be left uninsulated toensure that the semiconducting layer surrounding the conductor is at thesame potential as the conductor.

[0075] One advantage with circular conductor shapes and the divisioninto strands is that the harmonic currents are distributed very well. Itmay, therefore, be an advantage to have more strands in the conductorwhen harmonic currents may arise than when the current is moresinusoidal.

[0076] It is known that a high-voltage cable for transmission ofelectric energy is composed of conductors with extruded insulation withan inner and an outer semiconductor part. During transmission ofelectric energy, the starting-point has long been that the insulationshould be free from defects.

[0077] Isulation of a conductor for a rotatingsingle-winding/multiple-winding machine according to the invention maybe applied in some other way than by means of extrusion, for example byspraying or the like. It is important, however, that the insulationshould exhibit similar thermal properties through the whole crosssection. The semiconducting layers may be supplied with the insulationin connection with the insulation being applied to the conductors.

[0078] Preferably, cables with a circular cross section are used amongother things, to obtain a better packing density, cables with adifferent cross section may be used.

[0079] To build up a voltage in the rotating high-voltagesingle-winding/multiple-winding machine, the cable is disposed inseveral consecutive turns in slots in the magnetic core.

[0080] When the rotating high-voltage single-winding/multiple-windingmachine is designed as a single-winding machine, it is normally utilizedfor six-pulse rectification. Nowadays, filter and module methods areavailable which cause the ripple on the rectified six-pulse voltage tobe kept within acceptable limits.

[0081] A rotating high-voltage multiple-winding machine may, inprinciple, be designed with an optional number of winding systems and anoptional number of phases. A preferred embodiment consists of a 2×3phase system, electrically displaced relative to each other by 30electrical degrees as is required for a 12-pulse rectification. Otherfeasible combinations are a 2×2 phase system, a 4×3 phase system, etc.

[0082] A rotating high-voltage single-winding/multiple-winding machineaccording to the invention may operate within a wide frequency range.For large machines it may be a question of a few hundred Hz whereas formachines within the lower power range, frequencies of up to a few kHzmay occur.

[0083] The winding can be designed as a multi-layer concentric cablewinding to reduce the number of coil-end crossings. The cable may bemade with tapered insulation to utilize the magnetic core in a betterway, in which case the shape of the slots may be adapted to the taperedinsulation of the winding.

[0084] A significant advantage with a rotating high-voltagesingle-winding/multiple-winding machine according to the invention isthat the E field is near zero in the coil-end region outside the outersemiconductor and that with the outer casing at ground potential, theelectric field need not be controlled. This means that no fieldconcentrations can be obtained, neither within sheets, in coil-endregions, nor in the transition therebetween.

[0085] Devices according to the invention offer great possibilities ofintegration of parts included, such as semiconductor devices, coolingsystems, grounding systems, etc. This will be described in greaterdetail in connection with the description of embodiments.

[0086] The present invention also relates to a method of manufacturingthe magnetic circuit and, in particular, the winding. The method formanufacturing comprises disposing the winding in the slots by threadinga cable into the openings in the slots in the magnetic core. Since thecable is flexible, it can be bent and this permits a cable length to bedisposed in several turns in a coil. The coil ends will then consist ofbending zones in the cables. The cable may also be joined in such a waythat its properties remain constant over the cable length.

[0087] This method entails considerable simplifications compared withthe state of the art. The so-called Roebel bars are not flexible butmust be preformed into the desired shape.

[0088] Insulating windings and impregnation of the coils are alsoexceedingly complicated and expensive techniques when manufacturingrotating electric machines today.

[0089] A rotating high-voltage single-winding/multiple-winding machineaccording to the invention can also be designed as an air-gap-woundmachine without magnetic material or as a machine with magnetic materialin the back portion only.

[0090] To sum up, thus, a rotating high-voltagesingle-winding/multiple-winding machine with converters included in adevice for speed control according to the invention means a considerablenumber of important advantages in relation to corresponding prior artmachines. By high voltage are meant here voltages exceeding 10 kV and upto the voltage levels which occur for power networks. An importantadvantage is that a chosen potential, for example ground potential, hasbeen consistently conducted along the whole winding, which means thatthe coil-end region can be made compact and that bracing means in thecoil-end region can be applied at practically ground potential or anyother chosen potential. Still another important advantage is thatoil-based insulation and cooling systems disappear. This means that nosealing problems may arise and that the dielectric ring previouslymentioned is not needed. One advantage is also that all forced coolingcan be made at ground potential. A considerable space and weight savingfrom the installation point of view is obtained with a rotatinghigh-voltage single-winding/multiple-winding machine according to theinvention, since it replaces a previous installation design with twotransformer stages. The very large and extensive bushings which areneeded in the converter transformers to withstand the high dc potentialto which bushings and windings are subjected are not needed with themachine concept according to the invention. The invention requires nosuperconducting rotor with the problems associated therewith, such asmaintaining the temperature, encapsulation, and the like.

[0091] As is clear from the title of this invention, the inventioncomprises achieving a high-voltage variable-speed electric machinedrive. For this alternative, the above-mentioned power conversionbetween AC and AC is suitably used, which means ac conversion/acconversion with an arbitrary ratio between the frequency, amplitude,phase position, and phase number of the voltages. Such an arrangementfunctions as a kind of “ac transformer” which is able to reduce orincrease the voltage, change frequencies and/or change phase numbers.The connection may have a pure AC/AC conversion, for example with amatrix converter, but may also be designed as a dc intermediate link.

[0092] The above-mentioned properties make the connection well suited tobe included in an installation for high-voltage variable-speed electricmachine operation together with the rotating high-voltage machineaccording to the invention. As will have been clear, according toconventional technique described above, the machine may be designed as atwo-winding machine with feeding via two three-phase systems withphase-shifted voltages. A connection for such high-voltage electricmachine operation is clear from FIG. 4a.

[0093]FIG. 4a shows an installation which is capable of serving both asa motor drive and as a generator drive. For economic and othertechnical/practical reasons, the currently maximum suitable voltagelevel of the machine windings amounts to 25-30 kV. As motor drive, powermay be obtained from an ac network which, for example, may be a 132 kVnetwork. The power conversion from alternating current with a fixedmains frequency to the variable voltage and frequency which are neededfor speed control takes place in the example shown via an AC/ACconversion with a dc intermediate link, at a higher voltage level than25-30 kV. The mains frequency is obtained via a transformer T3 with twosecondary windings to achieve two voltage systems shifted 30 electricaldegrees relative to each other. These two systems each feed an AC/DCconverter, AC1 and AC2, respectively. The direct voltage from these isthen converted via the DC/AC converters AC3 and AC4 to two three-phasevoltages, shifted 30 electrical degrees relative to each other, with thevoltage and the frequency which are needed to drive the motor M and theload, for example a pump, with the desired speed.

[0094] If the connection according to FIG. 4a is to describe a generatordrive, the generator GF is driven by a turbine, and via the AC/AC powerconversion the windings of the transformer T3 may have such voltagesthat the ac network is fed with the desired voltage.

[0095] The connection according to FIG. 4a has four parallel dcconductors which are physically extended in parallel over a shortdistance. The dc conductors carry equal currents but in two directions.In case of a long transmission distance, a connection according to FIG.4b is to prefer, since two dc connections are eliminated when theconverters are series-connected. The connection according to FIG. 4bcauses the windings of the single-winding/multiple-winding machine to besubjected to dc potential.

[0096] The connection according to FIG. 4c is an improvement of theconnection in FIG. 3 and connects the converters in parallel, whichmeans that the windings of a single-winding/multiple-winding machine arenot subjected to dc potential.

BRIEF DESCRIPTION OF THE DRAWINGS

[0097]FIG. 1 shows a conventional HVDC transmitter station.

[0098]FIG. 2 shows an HVDC transmitter station with a so-called “DirectConnection”.

[0099]FIG. 3 shows a so-called interphase transformer connection.

[0100]FIGS. 4a, 4 b and 4 c show connections or high-voltage electricmachine drive according to the invention.

[0101]FIG. 5 shows the parts include in the current modified standardcabls.

[0102]FIG. 6 shows an embodiment of an axial end view of a sector/polepitch of a magnetic circuit according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0103] One important condition for being able to manufacture a magneticcircuit in accordance with the summary of the invention is to use forthe winding a cable with a semiconducting layer surrounding theconductor, which layer is surrounded by a layer of solid electricinsulation and a semiconducting layer surrounding the solid layer. Suchcables are available as standard cables for other power engineeringfields of use. To be able to describe an embodiment, initially a shortdescription of a standard cable will be made. The inner current-carryingconductor comprises a number of non-insulated strands. Around thestrands there is a semiconducting inner casing. Around thissemiconducting inner casing, there is an insulating layer of solidinsulation. An example of such solid insulation is XLPE or,alternatively, so-called EP rubber such as silicone rubber,thermoplastic resins or crosslinked thermoplastic resins. Thisinsulating layer is surrounded by an outer semiconducting layer which,in turn, is surrounded by a metal shield and a sheath. Such a cable willbe referred to below as a power cable.

[0104] A rotating high-voltage single-winding/multiple-winding machinehas as windings a cable, a preferred embodiment of which is shown inFIG. 5. The cable 1 is described in the figure as comprising acurrent-carrying conductor 2 which comprises transposed bothnon-insulated and insulated strands. Electromechanically transposed,solid insulated strands are also possible. Around the conductor there isan inner semiconducting casing 3 which, in turn, is surrounded by asolid insulating layer 4. This layer is surrounded by an outersemiconducting layer 5. The cable used as a winding in the preferredembodiment has no metal shield and no external sheath. To avoid inducedcurrents and losses associated therewith in the outer semiconductor,this may be cut off, preferably in the coil end, that is, somewhere inthe transitions from the stack of sheets to the end windings. Eachcut-off part is then connected to ground, whereby the outersemiconductor will be maintained at, or near, ground potential in thewhole cable length. This means that, around the solid insulated windingat the coil ends, the contactable surfaces, and the surfaces which aredirty after some time of use, only have negligible potentials to ground,and they also cause negligible electric fields.

[0105] To optimize a rotating high-voltagesingle-winding/multiple-winding machine, the design of the magneticcircuit as regards the slots and the teeth, respectively, is of decisiveimportance. In the embodiment with a threaded cable, the slots should beconnected as close to the casing of the coil sides as possible. It isalso desirable that the teeth at each radial level are as wide aspossible. This is important to minimize the losses, the magnetizationrequirement, etc., of the machine.

[0106] With access to a conductor for the windings as theabove-mentioned cable, there are great possibilities of being able tooptimize the magnetic core from several points of view. In thefollowing, a magnetic circuit in the stator of the rotating high-voltagesingle-winding/multiple-winding machine is referred to. FIG. 6 shows anembodiment of an axial end view of a sector/pole pitch 6 of a machineaccording to the invention. The rotor with the rotor pole is designated7. In conventional manner, the stator is composed of a laminated core ofelectric sheets successively composed of sector-shaped sheets. From aback portion 8 of the core, located at the radially outermost end, anumber of teeth 9 extend radially inwards towards the rotor. Between theteeth there are a corresponding number of slots 10. The use of cables 11according to the above among other things permits the depth of the slotsfor high-voltage machines to be made larger than what is possibleaccording to the state of the art. The slots have a cross sectiontapering towards the rotor since the need of cable insulation becomeslower for each winding layer towards the rotor. As is clear from thefigure, the slot substantially consists of a circular cross section 12around each layer of the winding with narrower waist portions 13 betweenthe layers. With some justification, such a slot cross section may bereferred to as a “cycle chain slot”. Since in such a high-voltagemachine, a relatively large number of layers will be needed, and thesupply of relevant cable dimensions as far as insulation and outersemiconductors are concerned is limited, it may in practice be difficultto achieve a desired continuous tapering of the cable insulation and thestator slot, respectively. In the embodiment shown in FIG. 6, cableswith three different dimensions of the cable insulation are used,arranged in three correspondingly dimensioned sections 14, 15 and 16,that is, in practice a modified cycle chain slot will be obtained. Thefigure also shows that the stator tooth can be shaped with a practicallyconstant radial width along the depth of the whole slot.

[0107] In an alternative embodiment, the cable which is used as awinding may be a conventional power cable as the one described above.The grounding of the outer semiconducting shield then takes place bystripping the metal shield and the sheath of the cable at suitablelocations.

[0108] The scope of the invention accommodates a large number ofalternative embodiments, depending on the available cable dimensions asfar as insulation and the outer semiconductor layer etc. are concerned.Also embodiments with so-called cycle chain slots can be modified inexcess of what has been described here.

[0109] As mentioned above, the magnetic circuit may be located in thestator and/or the rotor of the rotating high-voltagesingle-winding/multiple-winding machine. However, the design of themagnetic circuit will largely correspond to the above descriptionindependently of whether the magnetic circuit is located in the statorand/or the rotor. As mentioned in the introductory part of thedescription, the machine may be designed as an air-gap-wound machinewithout magnetic material or with magnetic material in the back portiononly.

[0110] As windings, windings are preferably used which may be describedas multilayer, concentric cable windings. Such windings mean that thenumber of crossings at the coil ends has been minimized by placing allthe coils within the same group radially outside one another. This alsopermits a simpler method for the manufacture and the threading of thestator winding in the different slots. If the machine is made as amachine with salient poles, the winding/windings will be wound aroundthe salient poles.

[0111] In an alternative embodiment of the rotating high-voltagesingle-winding/multiple-winding machine, the cable may be wound aroundsalient poles in a way which resembles an embodiment of a high-voltagetransformer according to Swedish patent application 9700335-4.

[0112] In the examples of embodiments of single-winding/multiple-windingmachines illustrated here, embodiments with a radial flux and axialwinding currents have been used. Single-winding/multiple-windingmachines with an axial air-gap flux and radial winding currents may alsobe designed in a way similar to that of low-voltage machines usingpresent-day technique.

[0113] In one embodiment of an installation according to the invention,the semiconductor devices may constitute an integral part of thehigh-voltage single-winding/multiple-winding machine.

[0114] The single-winding/multiple-winding machine and the semiconductordevices may have a common cooling system.

[0115] The single-winding/multiple-winding machine and the semiconductordevices shall have the same, and common, ground connection.

1. An installation comprising a rotating high-voltagesingle-winding/multiple-winding machine and a converter, characterizedin that a mechanical torque is converted into direct current and directvoltage via the converter without intermediate transformers and/orreactors.
 2. An installation according to claim 1, characterized in thatthe converter comprises semiconductor devices which are connected andfunction as an AC/DC converter.
 3. An installation comprising a rotatinghigh-voltage single-winding/multiple-winding machine and a converter,characterized in that direct current and direct voltage are convertedvia the converter into a mechanical torque without intermediatetransformers and/or reactors.
 4. An installation according to claim 3,characterized in that the converter comprises semiconductor deviceswhich are connected and function as a DC/AC converter.
 5. Aninstallation according to claims 1 and 2, characterized in that to theAC/DC rectifier there is connected a DC/AC inverter with directconnection to an ac network without intermediate transformers and/orreactors.
 6. An installation according to claims 3 and 4, characterizedin that to the dc side of the DC/AC inverter there is connected a DC/ACrectifier with direct connection to an ac network without intermediatetransformers and/or reactors.
 7. An installation according to claims 2and 4, characterized in that to the semiconductor devices may consist ofthyristors, diodes, triacs, gate turn-off thyristors (GTO), bipolartransistors (BJT), PWM transistors, MOSFET, insulated gate bipolartransistors (IGBT), static induction transistors (SIT), static inductionthyristors (SITH), MOS-controlled thyristors (MCT) and similarcomponents with semiconductor properties.
 8. An installation accordingto claims 1, 2, 3 and 4, characterized in that the converters constitutean integral part of the rotating high-voltagesingle-winding/multiple-winding machine.
 9. An installation according toclaims 1, 2 and 5, characterized in that the converters constitute anintegral part of the rotating high-voltagesingle-winding/multiple-winding machine.
 10. An installation accordingto claims 1, 2 and 6, characterized in that the converters constitute anintegral part of the rotating high-voltagesingle-winding/multiple-winding machine.
 11. An installation accordingto claims 1, 2 and 5, characterized in that the rotating high-voltagesingle-winding/multiple-winding machine and the semiconductor deviceshave a common cooling system.
 12. An installation according to claims 1,2 and 6, characterized in that the rotating high-voltagesingle-winding/multiple-winding machine and the semiconductor deviceshave a common cooling system.
 13. An installation according to claims 1,2 and 5, characterized in that the rotating high-voltagesingle-winding/multiple-winding machine and the semiconductor deviceshave the same and common ground connection.
 14. An installationaccording to claims 1, 2 and 6, characterized in that the rotatinghigh-voltage single-winding/multiple-winding machine and thesemiconductor devices have the same and common ground connection.
 15. Aninstallation according to claims 1 and 3 and wherein the rotatinghigh-voltage single-winding/multiple-winding machine comprises amagnetic circuit with one or more magnetic cores and one or morewindings phase-shifted in space, characterized in that the windingscomprise one or more current-carrying conductors (2), that around eachconductor there is arranged a first layer (3) with semiconductingproperties, that around the first layer there is arranged a solidinsulating layer (4), and that around the insulating layer there isarranged a second layer (5) with semiconducting properties.
 16. Arotating high-voltage single-winding/multiple-winding machine accordingto claim 15, characterized in that the first layer (3) is atsubstantially the same potential as the conductor.
 17. A rotatinghigh-voltage single-winding/multiple-winding machine according to claim15, characterized in that the second layer (5) is arranged in such a waythat it constitutes an equipotential surface surrounding theconductor/conductors.
 18. A rotating high-voltagesingle-winding/multiple-winding machine according to claim 15,characterized in that the second layer (5) is connected to groundpotential.
 19. A rotating high-voltage single-winding/multiple-windingmachine according to claim 15, 16, 17 or 18, characterized in that, forthe winding, all the semiconducting layers and insulating layers exhibitsimilar thermal properties, such that, upon a thermal movement in thewinding, no defects, cracks, or the like, occur in the insulating parts.20. A rotating high-voltage single-winding/multiple-winding machineaccording to claim 15, characterized in that the current-carryingconductor comprises a number of strands, whereby only a small number ofthe strands are non-insulated from each other.
 21. A rotatinghigh-voltage single-winding/multiple-winding machine wherein themagnetic circuit comprises a magnetic core and one or more windingsphase-shifted in space, characterized in that the windings comprise acable including one or more current carrying conductors (2), that eachconductor comprises a number of strands, that around each conductorthere is arranged an inner semiconducting layer (3), around which thereis arranged an insulating layer (4) of solid insulation, around whichthere is arranged an outer semiconducting layer (5).
 22. A rotatinghigh-voltage single-winding/multiple-winding machine with a magneticcircuit according to claim 21, characterized in that the cable alsocomprises a metal shield and/or a protective layer.
 23. A rotatinghigh-voltage single-winding/multiple-winding machine according to claim21, characterized in that the magnetic circuit is arranged in the statorand/or the rotor of the rotating electric machine.
 24. A rotatinghigh-voltage single-winding/multiple-winding machine according to claim21, characterized in that the outer semiconducting layer (5) is cut offinto a number of parts which are separately connected to groundpotential.
 25. A rotating high-voltage single-winding/multiple-windingmachine according to claim 21, 22, 23 or 24, characterized in that withconnection of the outer semiconducting layer to ground potential, theelectric field of the machine outside the semiconducting layer both inthe slots and in the coil-end region will be near zero.
 26. A rotatinghigh-voltage single-winding/multiple-winding machine according to claims21 and 22, characterized in that, when the cable comprises severalconductors, these are transposed.
 27. A rotating high-voltagesingle-winding/multiple-winding machine with a magnetic circuitaccording to claim 21, characterized in that the current-carryingconductor/conductors (2) comprise both non-insulated and insulatedwires, stranded into a number of layers.
 28. A rotating high-voltagesingle-winding/multiple-winding machine with a magnetic circuitaccording to claim 21, characterized in that the current-carryingconductor/conductors (2) comprise both non-insulated and insulatedstrands, transposed into a number of layers.
 29. A rotating high-voltagesingle-winding/multiple-winding machine with a magnetic circuitaccording to claim 21, characterized in that the slots (10) are formedas a number of cylindrical openings (12), extending axially and radiallyoutside one another, with a substantially circular cross sectionseparated by a narrower waist portion (13) between the cylindricalopenings.
 30. A rotating high-voltage single-winding/multiple-windingmachine with a magnetic circuit according to claims 21 and 29,characterized in that the substantially circular cross section of thecylindrical openings (12) of the slots, counting from a back portion (8)of the laminated core, is designed with a continuously decreasingradius.
 31. A rotating high-voltage single-winding/multiple-windingmachine with a magnetic circuit according to claims 21 and 29,characterized in that the substantially circular cross section of thecylindrical openings (12) of the slots, counting from a back portion (8)of the laminated core, is designed with a discontinuously decreasingradius.
 32. A rotating high-voltage single-winding/multiple-windingmachine wherein the magnetic circuit comprises a magnetic core and oneor more windings, phase-shifted in space, characterized in that themagnetic core is formed with salient poles.
 33. A rotating high-voltagesingle-winding/multiple-winding machine, characterized in that it isair-gap-wound.
 34. A rotating high-voltagesingle-winding/multiple-winding machine, characterized in that theair-gap flux is radial.
 35. A rotating high-voltagesingle-winding/multiple-winding machine, characterized in that theair-gap flux is axial.
 36. A method for manufacturing a rotatinghigh-voltage single-winding/multiple-winding machine comprising amagnetic circuit comprising a magnetic core comprising slots, channelsor the like, whereby these slots etc. have at least one opening,accessible from the outside of the magnetic core, and a winding,characterized in that the winding is flexible and is threaded into theopening.
 37. A method for manufacturing a magnetic circuit for arotating high-voltage single-winding/multiple-winding machine, whereinthe magnetic circuit is arranged in the stator and/or rotor of therotating electric machine, which magnetic circuit comprises a magneticcore (8) with slots (10) for two or more windings (1), phase-shifted inspace, and wherein the slots are formed as cylindrical openings (12),extending axially and radially, outside one another, with asubstantially circular cross section, the method being characterized inthat the winding comprises a cable which is threaded into thecylindrical openings.
 38. A method for manufacturing a magnetic circuitfor a rotating high-voltage single-winding/multiple-winding machine,wherein the magnetic circuit is arranged in the stator and/or rotor ofthe rotating electric machine and is formed as salient poles, the methodbeing characterized in that the winding comprises a cable which is woundaround the salient poles.